function animate(who,where,callback) {
    var timer1 = setInterval(function(){
        var step = (where-who.offsetLeft)/10;
        step = step > 0 ? Math.ceil(step) : Math.floor(step); //用于判断数值为正或者负的时候的 取值
        if (who.offsetLeft == where){
            clearInterval(timer1);
            if (callback){
                callback();
            }
        } 
            who.style.left = who.offsetLeft + step + 'px'; 
    },10)
}